Semiconductor chips are widely used in a variety of industrial applications. They are generally based on silicon as a semiconductor substrate into which semiconductor components are integrated in numerous operations. The production of semiconductor chips is therefore complicated and expensive. The discovery of electrically conductive organic compounds has opened the path to microelectronic components, which are no longer based on inorganic semiconductor materials but on synthetically obtainable organic polymers. Owing to the variability of their structure, these compounds permit the development of materials which are optimized especially for a specific application. Many microelectronic components, such as light emitting diodes or transistors, which demonstrate the suitability of these organic materials for the production of highly integrated circuits, have also already been developed. Some of these components, such as, for example, light emitting diodes, have already reached such a high level of development that industrial production appears possible. However, the material development for volatile or nonvolatile memories based on organic polymers and molecules is still substantially at the research stage. In A. Bune et al., Appl. Phys. Lett. 67 (26) (1995) 3975, and A. Bune et al., Nature 391 (1998) 874, it was shown that materials based on PVDF (polyvinylidene difluoride), in particular a copolymer with trifluoroethylene (PVDF-PTrFE; 70:30), are suitable as materials for memory applications with medium to low density. The ferroelectricity of these materials is utilized for use as a storage medium.
To be able to achieve higher storage densities, the size of the individual memory elements has to be correspondingly reduced. In the case of a size of the structural elements of less than 100 nm, memories which are based on a change in the electrical resistance are preferred to memories based on ferroelectricity, since this can be more easily evaluated by means of an electrical technology. In Gao, H. J et al., Phys. Rev. Lett. 84 (2000) 1780-1783, a memory concept is described which is based on a donor-acceptor complex of 1,4-phenylenediamine and 3-nitrobenzalmalononitrile. For the storage information, the difference between the electrical conductivities of amorphous and crystalline phase is utilized. In Krieger H. Ju. et al., Syn. Met. 122 (2001) 199-202, a concept for the production of memories based on organic materials is described, in which the doping and dedoping of an organic π-conjugated semiconductor by salt additives is utilized in order to effect a change in the conductivity of layers. In Ma D. et al., Adv. Mater. 12(14) (2000) 1063-1066, a resistive memory element is described that includes (as a storage medium) a polymethacrylate derivative carrying anthracene side groups. The poly(methyl methacrylate-co-9-anthracenylmethyl methacrylate) exhibits a resistive hysteresis effect. On application of a voltage, the component exhibits electrical conductivity above a critical voltage (Vcrit.). If the applied voltage is then decreased again, the component remains electrically conductive until the voltage falls below a threshold voltage Vhold, below which the component returns to its nonconductive state.
At present, no memory elements based on organic materials are as yet available which make industrial production appear promising.